[git commit] decompress_gunzip: Fix DoS if gzip is corrupt

Denys Vlasenko vda.linux at googlemail.com
Fri Mar 12 09:45:10 UTC 2021

commit: https://git.busybox.net/busybox/commit/?id=f25d254dfd4243698c31a4f3153d4ac72aa9e9bd
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/master

On certain corrupt gzip files, huft_build will set the error bit on
the result pointer. If afterwards abort_unzip is called huft_free
might run into a segmentation fault or an invalid pointer to

In order to mitigate this, we check in huft_free if the error bit
is set and clear it before the linked list is freed.

Signed-off-by: Samuel Sapalski <samuel.sapalski at nokia.com>
Signed-off-by: Peter Kaestle <peter.kaestle at nokia.com>
Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
 archival/libarchive/decompress_gunzip.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/archival/libarchive/decompress_gunzip.c b/archival/libarchive/decompress_gunzip.c
index eb3b64930..e93cd5005 100644
--- a/archival/libarchive/decompress_gunzip.c
+++ b/archival/libarchive/decompress_gunzip.c
@@ -220,10 +220,20 @@ static const uint8_t border[] ALIGN1 = {
  * each table.
  * t: table to free
+#define BAD_HUFT(p) ((uintptr_t)(p) & 1)
+#define ERR_RET     ((huft_t*)(uintptr_t)1)
 static void huft_free(huft_t *p)
 	huft_t *q;
+	/*
+	 * If 'p' has the error bit set we have to clear it, otherwise we might run
+	 * into a segmentation fault or an invalid pointer to free(p)
+	 */
+	if (BAD_HUFT(p)) {
+		p = (huft_t*)((uintptr_t)(p) ^ (uintptr_t)(ERR_RET));
+	}
 	/* Go through linked list, freeing from the malloced (t[-1]) address. */
 	while (p) {
 		q = (--p)->v.t;
@@ -289,8 +299,6 @@ static unsigned fill_bitbuffer(STATE_PARAM unsigned bitbuffer, unsigned *current
  * or a valid pointer to a Huffman table, ORed with 0x1 if incompete table
  * is given: "fixed inflate" decoder feeds us such data.
-#define BAD_HUFT(p) ((uintptr_t)(p) & 1)
-#define ERR_RET     ((huft_t*)(uintptr_t)1)
 static huft_t* huft_build(const unsigned *b, const unsigned n,
 			const unsigned s, const struct cp_ext *cp_ext,
 			unsigned *m)

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